Many manufacturing and industrial applications benefit from fluid atomization to create a fine vapor mist or aerosol, such as ink print heads, three-dimensional (3D) part manufacturing, fuel/air mixing used in combustion applications, atomizing air-paint mixtures for spray painting, applying coatings to pharmaceuticals, applying adhesives to various objects and surfaces, and the like. Once a component solution is atomized it can be readily processed to coat virtually any shaped surface.
Regardless of the application, most spray deposition systems create droplets at a nozzle tip that have inherent directionality. The conventional spray systems use airblast, shear atomizers, upstream atomizers, and a variety of collimation methods (i.e., virtual impactors and sheath flow control) to focus and direct the spray into a nozzle and then to targeted deposition. Generally, in the context of a print head, for example, the aerodynamic, airflow velocities required to deposit droplets of a small size, in the order of 1 micron, is high, about 30-50 m/s for droplet throw distances on the order of a millimeter (mm).
One conventional spray deposition method uses lateral cross-flows in a shared manifold of multiple fluid ejectors. The lateral cross-flows likely generate flow instabilities and secondary flows at the cross-flow velocities required to successfully deposit the small droplets with high spatial precision for a 3D printing application. Alternatively, some other conventional spray deposition systems use multiple, dedicated feed lines to each ejector or jet and a specialized inlet design that requires dedicated, miniature aerosol jet arrays. However, such a dedicated, specialized system is complex and the manifold inlet design is vulnerable to clogging, especially with fluids having non-Newtonian properties like high-viscosity solutions commonly used in 3D part fabrication and polymer melts used in fused deposition modeling (FDM) systems. Many of the drawbacks of the current systems and methods are amplified in a system with multiple nozzles.
To help with directing and focusing droplets, some droplet deposition systems, such as spray or powder coating painting systems used to apply metallic paint to vehicles, use rotary atomizers coupled with external corona generators and electrically grounded parts to achieve an electrostatically-assisted spray process having a highly-efficient deposition of material and uniform coating. Similar corona charging systems are used with polymer powder coating devices. However, such systems suffer from charge build-up and require the parts to be grounded. The high surface voltage build-up leads to electrical breakdown across the coating and coating thicknesses must be limited to 10's to 100's of microns, depending on the system. Coating dielectric (plastic) parts remains difficult because of the lack of an available grounding path in the dielectric material. Electrostatic directing and focusing strategies are simply not suitable for and present too many challenges to be efficient for many applications, including 3D part fabrication and other printing applications.
Therefore, the spray deposition art would greatly benefit from systems and methods that can direct and focus spray droplets and facilitate aerodynamic spray deposition.